The present invention relates to aircraft engine thrust reverser systems and, more particularly, to a device used to limit the torque in an aircraft thrust reverser drive train.
When a jet-powered aircraft lands, the landing gear brakes and imposed aerodynamic drag loads (e.g., flaps, spoilers, etc.) of the aircraft may not, in certain situations, be sufficient to slow the aircraft down in the required amount of runway distance. Thus, jet engines on most aircraft include thrust reversers to enhance the braking of the aircraft. When deployed, a thrust reverser redirects the rearward thrust of the jet engine to a generally forward direction to decelerate the aircraft. Because the jet thrust is directed generally forward, the jet thrust also slows down the aircraft upon landing.
Various thrust reverser designs are commonly known, and the particular design utilized depends, at least in part, on the engine manufacturer, the engine configuration, and the propulsion technology being used. Thrust reverser designs used most prominently with turbofan jet engines fall into three general categories: (1) cascade-type thrust reversers; (2) target-type thrust reversers; and (3) pivot door thrust reversers. Each of these designs employs a different type of moveable thrust reverser component to change the direction of the jet thrust.
Cascade-type thrust reversers are normally used on high-bypass ratio jet engines. This type of thrust reverser is located on the circumference of the engine""s midsection and, when deployed, exposes and redirects air flow through a plurality of cascade vanes. The moveable thrust reverser components in the cascade design includes several translating sleeves or cowls (xe2x80x9ctranscowlsxe2x80x9d) that are deployed to expose the cascade vanes.
Target-type reversers, also referred to as clamshell reversers, are typically used with low-bypass ratio jet engines. Target-type thrust reversers use two doors as the moveable thrust reverser components to block the entire jet thrust coming from the rear of the engine. These doors are mounted on the aft portion of the engine and may form the rear part of the engine nacelle.
Pivot door thrust reversers may utilize four doors on the engine nacelle as the moveable thrust reverser components. In the deployed position, these doors extend outwardly from the nacelle to redirect the jet thrust.
The primary use of thrust reversers is, as noted above, to enhance the braking of the aircraft, thereby shortening the stopping distance during landing. Hence, thrust reversers are usually deployed during the landing process to slow the aircraft. Thereafter, when the thrust reversers are no longer needed, they are returned to their original, or stowed, position.
The moveable thrust reverser components in each of the above-described designs are moved between the stowed and deployed positions by actuators. Power to drive the actuators may come from one or more drive motors, or from a hydraulic or pneumatic fluid system connected to the actuators, depending on the system design. A drive train that includes one or more synchronization mechanisms, such as flexible rotating shafts, may interconnect the actuators (and drive motors, if included) to maintain synchronous movement of the moveable thrust reverser components.
Each of the above-described system configurations is robustly designed and is safe and reliable. Nonetheless, analysis has shown that secondary damage to various portions of the thrust reverser system may result under certain postulated conditions. For example, if one of the actuators becomes jammed, it is postulated that all of the driving force from the remaining operable actuators would be concentrated, via the synchronization mechanisms, on the jammed actuator. This postulated condition may result in damage to the actuator system components, including the motors (if included), actuators, synchronization mechanisms, or the moveable thrust reversers components.
One solution to above-described postulated condition is to include one or more torque limiters in the drive train that applies a brake when a predetermined torque magnitude in the drive train is attained. One such toque limiters is commonly implemented by attaching two plates between two shaft ends, and spring loading the plates together. Each plate may include a series of pockets that have ramped sides. A torque transmitting ball may be inserted into each of the pockets. These balls transmit torque between the two plates and are therefore under a shear force. If the torque is high enough to overcome the spring force, the balls roll along the ramped sides of the pockets causing the plates to spread apart and engage brake pads.
Although the torque limiters presently used in thrust reverser actuation systems are believed to be safe and reliable, each may exhibit certain drawbacks in particular situations. For example, some torque limiters have sliding surfaces that add friction losses, which may adversely affect the repeatability of the activation torque. Some torque limiters also transmit all of the operational torque through the torque transmitting balls, which can concentrate stress in the balls and thus adversely affect component size and weight. Additionally, some torque limiters are not suited for relatively high-speed applications, and still others are relatively complex and costly.
Hence, there is a need for torque limiter that addresses one or more of the drawbacks noted above. Namely, a torque limiter that does not have significant friction losses, which allows accurate, repeatable torque limiting, and/or a torque limiter that does not transmit all of the operational torque through the balls, and/or is compact and is relatively low is weight, and/or is relatively inexpensive and simple in design. The present invention addresses one or more of these needs.
The present invention provides a torque activated brake assembly, and a thrust reverser system that incorporates the brake assembly. The brake assembly has relatively low friction losses, which allows accurate and repeatable torque limiting operations. The brake assembly is also compact, constructed of a relatively small number of parts and, therefore, has a low rotating inertia. The brake assembly is additionally constructed so that the operational torque is not transmitted through the balls.
In one embodiment of the present invention, and by way of example only, a torque activated brake assembly includes a first plate, at least two grooves in the first plate, a second plate, at least two grooves in the second plate, at least two balls, and a torsion spring. The first plate has an interior side, an exterior side, and an opening extending therebetween. The grooves in the first plate are formed in the first plate interior side, and each have a cam surface located at a predetermined angle. The second plate has an interior side, an exterior side, and an opening extending therebetween, and the second plate interior side is positioned opposed to the first plate interior side. The grooves in the second plate are formed in the second plate interior side and are substantially aligned with at least two of the grooves in the first plate. The second grooves each have a cam surface located at a predetermined angle. The balls are positioned one each in the aligned grooves in the first and second plates. The torsion spring has a first end coupled within the first plate opening and a second end coupled within the second plate opening.
In another exemplary embodiment, a torque activated brake assembly includes a first plate, at least two grooves in the first plate, a second plate, at least two grooves in the second plate, at least two balls, a torsion spring, a housing, a first brake surface, and a second brake surface. The first plate has an interior side, an exterior side, and an opening extending therebetween. The grooves in the first plate are formed in the first plate interior side, and each have a cam surface located at a predetermined angle. The second plate has an interior side, an exterior side, and an opening extending therebetween, and the second plate interior side is positioned opposed to the first plate interior side. The grooves in the second plate are formed in the second plate interior side and are substantially aligned with at least two of the grooves in the first plate. The grooves in the second plate are formed in the second plate interior side, and each have a cam surface located at a predetermined angle. The balls are positioned one each in the aligned grooves in the first and second plates. The torsion spring has a first end coupled within the first plate opening and a second end coupled within the second plate opening. The housing surrounds at least a portion of the first and second plates. The first brake surface is mounted in the housing and is positioned a first predetermined distance from the first plate exterior side. The second brake surface is mounted in the housing and is positioned the first predetermined distance from the second plate exterior side. The first plate exterior side and the second plate exterior side contact the first brake surface and the second brake surface, respectively, when the balls are positioned along the groove cam surfaces a second predetermined distance from the first plate interior side and the second plate interior side.
In yet another exemplary embodiment, a control system for moving a thrust reverser includes at least one drive motor, at least two actuators, at least one synchronization mechanism, and a torque activated brake assembly. Each drive motor is operable to supply a driving force. Each actuator is operably coupled to receive the driving force from the motor to thereby move the thrust reverser between a stowed position and a deployed position. Each synchronization mechanism mechanically couples the actuators and is configured to maintain the actuators in substantial synchronization with one another upon receipt, by the actuators, of the driving force. The torque activated brake assembly is operably coupled between at least one drive motor and at least one synchronization mechanism, and is activated upon a predetermined torque value being reached between each operably coupled motor and synchronization mechanism. The brake assembly includes a first plate, at least two grooves in the first plate, a second plate, at least two grooves in the second plate, at least two balls, and a torsion spring. The first plate has an interior side, an exterior side, and an opening extending therebetween. The grooves in the first plate are formed in the first plate interior side, and each have a cam surface located at a predetermined angle. The second plate has an interior side, an exterior side, and an opening extending therebetween, and the second plate interior side is positioned opposed to the first plate interior side. The grooves in the second plate are formed in the second plate interior side and are substantially aligned with at least two of the grooves in the first plate. The second grooves each have a cam surface located at a predetermined angle. The balls are positioned one each in the aligned grooves in the first and second plates. The torsion spring has a first end coupled within the first plate opening and a second end coupled within the second plate opening.
In still a further exemplary embodiment, a control system for moving a thrust reverser includes at least two actuators, at least two synchronization mechanisms, and a torque activated brake assembly. Each actuator is operably coupled to receive a driving force to thereby move the thrust reverser between a stowed position and a deployed position. Each synchronization mechanism mechanically couples the actuators and is configured to maintain the actuators in substantial synchronization with one another upon receipt, by the actuators, of the driving force. The torque activated brake assembly is operably coupled between at least two synchronization mechanisms, and is activated upon a predetermined torque value being reached between the operably coupled synchronization mechanisms. The brake assembly includes a first plate, at least two grooves in the first plate, a second plate, at least two grooves in the second plate, at least two balls, and a torsion spring. The first plate has an interior side, an exterior side, and an opening extending therebetween. The grooves in the first plate are formed in the first plate interior side, and each have a cam surface located at a predetermined angle. The second plate has an interior side, an exterior side, and an opening extending therebetween, and the second plate interior side is positioned opposed to the first plate interior side. The grooves in the second plate are formed in the second plate interior side and are substantially aligned with at least two of the grooves in the first plate. The second grooves each have a cam surface located at a predetermined angle. The balls are positioned one each in the aligned grooves in the first and second plates. The torsion spring has a first end coupled within the first plate opening and a second end coupled within the second plate opening.
In other exemplary embodiments, novel thrust reverser brake plate and torsion springs are also disclosed. The configurations of these components is described above.